How much off-contact do I need?
Depending on the screen tension, the off-contact should be 1/16 to 1/8 of an inch for t-shirts and thinner garments. For thicker garments like hoodies and fleece, you'd double the measurement. Experiment to discover what is the right height for your setup. Your goal is to have the screen low as it can go while still being able to snap up without getting stuck.
While a general statement of ⅛ inch off contact is usually thrown around here. It does not mean that ⅛ will work for you. What you want to see is enough off contact so that the screen snaps off the print as quickly as possible. If the screen is sticking to your print at ⅛ then you need to slowly increase your off contact UNTIL the screen does snap off. If you find you need to create exceptional off contact, your screen tension is probably too low and you should replace the screen soon.